1. Field of the Invention
The present invention relates to a schottky barrier diode. Particularly, the present invention relates to technology of improving the reverse surge capacity of a schottky barrier diode.
Priority is claimed on Japanese Patent Application No. 2011-049621, filed Mar. 7, 2011, the content of which is incorporated herein by reference.
2. Description of the Related Art
Schottky barrier diodes (hereinafter referred to as “SBD”) are semiconductor elements using rectification behavior of schottky barrier caused by schottky junction between a semiconductor layer and a metal layer. The SBDs are characterized by faster operation and smaller forward voltage drop than general p-n junction diodes.
Regarding switching power sources including such SBDs, reverse voltage applied in a direction from an n-type semiconductor layer to a metal layer exceeds the upper voltage limit of the SBD (hereinafter referred to as “reverse surge capacity”) in some cases, such as in a case of emergency stop in emergency situations. If the reverse voltage exceeds the reverse surge capacity, the SBD might break down.
As an example of diodes improving the reverse surge capacity, diodes having such a junction barrier schottky (hereinafter referred to as “JBS”) structure as shown in FIG. 4 are well known.
FIG. 4 illustrates an example of a JBS diode of related art. A JBS diode 100 includes: an n-type semiconductor layer 102 formed on a surface of a semiconductor substrate 101 made of silicon carbide (SiC) or the like; and a metal layer 103 forming a schottky junction with the n-type semiconductor layer 102. Additionally, an insulating layer 104 is formed over the n-type semiconductor layer 102 so as to extend outward from a periphery region of the metal layer 103. Further, a guard ring layer 105 is formed in the n-type semiconductor layer 102 so as to overlap a connecting portion between the metal layer 103 and the insulating layer 104, that is, a periphery region of the insulating layer 104. The guard ring layer 105 is formed by ion implantation of an impurity into the n-type semiconductor layer 102. The guard ring layer 105 reduces field concentration which occurs in a peripheral region of the n-type semiconductor layer 102 and the metal layer 103 that form the schottky junction.
On the other hand, the JBS structure is formed inside the guard ring layer 105, that is, in a center region. For example, multiple second semiconductor layers 106 made of a p-type semiconductor are formed at a predetermined interval, inside the guard ring layer 105. The second semiconductor layers 106, which form p-n junction with the n-type semiconductor layer 102, are designed so as to be lower in voltage than the portion of the schottky junction between the n-type semiconductor layer 102 and the metal layer 103, and the insulating layer 104 therearound. Accordingly, the load of reverse current (reverse surge) is induced on the JBS diode including the second semiconductor layers 106, thereby improving the reverse surge capacity of the schottky junction portion (see, for example, Material Science Forum Vols. 527-529 (2006), pp 1155-1158).
Regarding the aforementioned JBS diode of the related art, however, the p-type second semiconductor layers are disposed close to the portion of the schottky junction between the n-type semiconductor layer and the metal layer. For this reason, a depletion layer extends from the schottky junction portion along the second semiconductor layers. Thereby, it is difficult to sufficiently reduce the voltage of the second semiconductor layers. Consequently, field concentration in the peripheral region is not actually reduced for the SBD having such a JBS structure as that of the related art. Therefore, the reverse surge capacity is not improved.